In the formation of micro mechanical devices, commonly referred to as MEMS devices, silicon or other semiconductor materials are used to form small structures. Semiconductor fabrication techniques are used to form the structures. One such technique is the use of wet chemical etching of the silicon to remove silicon in a controlled manner. Precise control of the etching is required to form critical dimensions required for some of the structures. An “etch stop” is used to achieve this control. One type of etch stop is accomplished by heavily doping a desired portion of the semiconductor with boron, and etching in an anisotropic etchant such as EDP or KOH. When the etchant reaches the heavily doped layer, the etch rate slows down by several orders of magnitude, effectively stopping the etching.
Metal layers are added to MEMS devices prior to etching to provide electrical contact with the silicon. The metal layers provide a good electrical contact but are not attacked by the etchant.